Sitting in the MirrorBrain talk at FOSDEM, taking notes.
Actively used since ~2007.
Split between the redirector and the tester, explicitly made separate.
SourceForge helped with the ASN/Closest-Network side.
Metalinks and P2P support.
Scans mirrors for filelist to see what's present.
Load limiting by making director support mirrors that are limited to a local network / AS / country etc.
MetaLinks don't have Magnet links presently, but I noted that it should be possible to include it.
Using GeoDNS directly for lookups can cause trouble with partial mirrors. Ideally need to put a MirrorBrain server on each continent/region, and GeoDNS to point to that. Also, from some countries, bandwidth to adjcaent countries that might have a mirror is MUCH worse than bandwidth to a well-connected country elsewhere. Past user experience noted with a user in Mozambique, for whom the fastest mirror was via satellite to Canada. Routing data IS needed to make that best choice.
MirrorBrain mailing lists also have a generic non-project-specific "networkers" list for talk between content providers and mirror admins, non-specific to any app.